Purpose: Assess Lm isolated from Ready-to-Eat (RTE) food processing environments (FPE) in British Columbia (BC) for characteristics associated with either increased risk of causing disease or treatment failure.
Methods: Lm (n = 36) isolates from BC RTE FPE were serotyped and virulence gene inlA was profiled. Isolates were also screened for the 50-kbp Listeria genomic island 1 (LGI1) associated with epidemic clone V strains that have caused illness across Canada. Conventional PCR was used to amplify inlA and LGI1. InlA amplicons were subjected to Sanger sequencing and these data were examined for the presence of virulence attenuating mutations, while LGI1 amplicons were visualized using agarose gel electrophoresis. Antimicrobial resistance was assessed using a disc diffusion assay with a panel of 18 antimicrobials.
Results: Most isolates (97%) belonged to serotypes commonly linked to listeriosis and possessed full-length inlA (81%) or a 3-codon deletion at aa741-743 (17%) that is not thought to result in loss of virulence. One isolate contained a novel mutation in inlA resulting in a premature stop codon at aa760. LGI1 was absent in all isolates. Resistance was observed in all isolates for cefoxitin and nalidixic acid. Most isolates were resistant to clindamycin (94%) and 92% and 67% showed intermediate resistance to ciprofloxacin and vancomycin, respectively. All isolates were susceptible to the remaining antibiotics.
Significance: These results show that Lm strains recovered from BC FPE may be capable of causing Listeriosis if transferred to RTE foods. While these results may seem concerning, the high-risk strains identified here did not show resistance to antibiotics commonly used to treat Listeriosis.